Chronic obstructive pulmonary disease (COPD) affects 10 million Americans and is increasing in prevalence and as a cause of death and disability. Although the disease can be identified in the asymptomatic phase, little is known about interventions to arrest the accelerated decline in lung function, which eventually leads to disability. Inflammation of the peripheral airways is a histologic hallmark of this disorder, and it is thought that this inflammation leads to the clinical manifestations of the disease--alveolar wall destruction (emphysema) and bronchial hyperreactivity (bronchospasm). It is not known whether inhaled anti- inflammatory agents, in particular, inhaled corticosteroids, can alter the natural history of this disease or reduce morbidity and mortality. The present study is designed to determine, in a multi-center placebo- controlled clinical trial, whether the use of an inhaled corticosteroid (triamcinolone acetonide 400 micrograms twice daily) can alter the accelerated decline in lung function. Ten clinical centers throughout North America will enrol 1,540 participants with mild to moderate COPD who have previously had 5-years of monitoring of lung function and bronchial reactivity in the Lung Health Study. Half of the participants will be assigned active drug, and half an identical-appearing placebo. All smoking participants who express interest will receive smoking cessation counseling. Spirometry will be measured every six months for up to 4 1/2 years to determine whether the treatment will alter the decline in lung function. In addition, bronchial reactivity, respiratory symptoms, morbidity, mortality, and quality of life will be measured to determine whether the intervention improves health status. Secondary objectives of the study will be to determine whether this intervention has adverse effects, to measure the patterns of adherence with the drug, and to determine whether there are certain subgroups of people who benefit or are susceptible to adverse effects.